1. Field of the Invention
The present invention relates to an optical switching system and, more particularly, to an optical switching system advantageously applicable to an optical local area network.
2. Description of the Prior Art
An optical switch is a promising substitute for an electronic switching system in the communication systems art. An optical switching system having an optical transmission path for propagating signal beams and a plurality of optical nodes optically connected to the path for interchanging the signal beams is now under study for implementing an optical communication system. Use may be made of signal beams having a single wavelength or multiplexed wavelengths. Such an optical switching system is disclosed in, for example, Ikutaro Kobayashi "Future Trends of Photonic Switching Systems", the Institute of Electronics, Information and Communication Engineers of Japan, Technical Research Report, Optics and Quantum Electronics Study Meeting, OQE 87-167, pp. 53-56 Feb. 22, 1988). Peter Cochrane et al outlines the past optical systems using optical fibers and the development of future passive optical networking in "Future Optical Fiber Transmission Technology and Networks", IEEE Communications Magazine, November 1988, pp. 45-70. A method and an apparatus for optical communication of the kind using coherent detection is taught in Japanese Patent Laid-Open Publication No. 159929/1987, corresponding to U.S. patent application Ser. No. 815,073, now U.S. Pat. No. 4,742,576 filed on Dec. 23, 1985 in the name of Donald H. MacMahon (now U.S. Pat. No. 4,742,576).
A switching system of the type using signal beams having a single wavelength has the drawback that the transmission capacity available therewith is limited. The problem with an optical switching system using signal beams having multiplexed wavelengths heretofore proposed is that closely spaced wavelengths are not achievable because the wavelength of the signal beam to be generated differs from one node to another. This prevents the number of channels and, therefore, the transmission capacity, from being increased because the wavelength range available with an optical fiber constituting an optical transmission path is limited.